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本文用X-光光电子谱(XPS)、扫描俄歇显微分析(SAM)、透射电镜(TEM)的电子微衍射(EMD)技术、原子吸收光谱(AAS)等方法考察了新鲜的和经过170多小时使用、活性明显下降的Ag_xSb_yO_z/SiO_2催化剂的化学组成、元素分布及其晶相结构的变化。发现活性明显下降的催化剂和新鲜的相比,催化剂表面发生了更严重的银表面偏析;Ag和Sb由同步分布变成了非同步分布;其活性组分的晶相结构发生了明显变化:由原来的以AgSbO_3和Sb_2O_4为主的晶相变成了以Sb_2O_3和Ag为主的晶相。由模型催化剂知Sb_2O_4/SiO_2为非活性的;因此,该催化剂对异丁烯—甲醛缩合制异戊二烯反应的活性相似乎为AgSbO_3。经过较长时间的、多次反应—再生循环,催化剂的活性组份被部分还原,且不能在现有再生条件下完全复原,逐渐破坏了该活性相,从而逐渐丧失其催化活性。
In this paper, X-ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), transmission electron microscopy (TEM) electron micro-diffraction (EMD) technology, atomic absorption spectroscopy (AAS) The chemical composition, elemental distribution and crystal phase structure of Ag_xSb_yO_z / SiO_2 catalyst with obvious reduction of activity after many hours of use were observed. Compared with the fresh catalyst, the catalyst showed a more serious silver surface segregation. The Ag and Sb phases changed from synchronous to asynchronous, and the crystal structure of the active components changed significantly from The original AgSbO_3 and Sb_2O_4-based crystal phase into Sb_2O_3 and Ag-based crystal phase. The model catalyst is known as Sb 2 O 4 / SiO 2 is inactive; therefore, the activity of the catalyst for the reaction of isobutylene-formaldehyde condensation to isoprene appears to be AgSbO 3. After a long period of multiple reaction-regeneration cycles, the active component of the catalyst is partially reduced and can not fully recover under the existing regeneration conditions, gradually destroying the active phase and gradually losing its catalytic activity.